Makes the inheritance_column api documentation visible [ci-skip]

[jean-francois-labbe]

Summary

This PR makes the inheritance_column searchable in the api documentation.

When trying to configure Single table inheritance for a model. I knew I could configure the column name. I couldn't find it in the api search bar. I expected to find it using the inheritance word.
The inheritance_column is mentioned here https://api.rubyonrails.org/classes/ActiveRecord/Inheritance.html.

The current 'inheritance' search yields

With this change it yields

[jonathanhefner]

This only documents the setter. Should we split this into getter and setter documentation, a la implicit_order_column and implicit_order_column=?

[jean-francois-labbe]

I split the documentation one part for inheritance_column and another forinheritance_column=

[jean-francois-labbe]

I've got a quick question about the way we declare the inheritance_column.
It requires the use to the self keyword.
When comparing how we declare associations, the has_many, belongs_to do not require self keyword.

class Car < ApplicationRecord
  self.inheritance_column = 'car_type'

  has_many :parts
end

Is there a reason why we need to write it this waysself.inheritance_column = 'car_type' instead of inheritance_column :car_type ?

class Car < ApplicationRecord
  inheritance_column :car_type

  has_many :parts
end

I'd like to understand the reason behind this.

[jonathanhefner]

I'm not sure if I understand your question.

Are you asking why we need to write self.? That is necessary because inheritance_column is implemented as a class attribute. If we wrote just inheritance_column = "foo", it would set a local variable inheritance_column instead of MyClass.inheritance_column. (It's the same as with attr_writer.)

Or are you asking why inheritance_column was implemented as a class attribute instead of another way? In that case, I do not have an objective answer.

[jonathanhefner]

Thank you, @jean-francois-labbe! 😃

(Backported to 7-0-stable.)